A standard hammer-drill chuck has a chuck body that can be connected to a drill spindle and in which jaws forming a seat between themselves for the drilling tool are arranged in guide grooves running at an angle to the chuck axis, the jaws engaging with a row of teeth for opening and closing the drill chuck into the screwthread of a threaded ring rotatably guided on the chuck body, furthermore with a locking mechanism for the threaded ring consisting of a coaxial annular array of locking recesses and of least one locking member that is engaged in the locking position under the force of a locking spring in the locking recesses, locking member and the locking recesses engaging each other with inclined flanks in such a manner that they block the threaded ring against rotation in the direction of rotation corresponding to the opening of the drill chuck but when the threaded ring is rotated in the opposite direction of rotation, that is, the one corresponding to the closing of the drill chuck they press the locking member against the force of the locking spring out of the locking recesses and thus allow it to slide from locking recess to locking recess, furthermore with a coaxial tightening ring that can rotate between first abutments in a limited manner opposite the threaded ring, and with a latch forming two angularly offset latching positions for the tightening ring or sleeve.
Such a drill chuck is known from EP 0 710 518 A2 that has proven itself excellent in practice and has been sold in large numbers on account of its robustness and reliability. These previously cited advantages are associated with a very simple operation for the user since the locking mechanism is automatically actuated when loosening and tightening the drill chuck, that is, the user only has to grasp the tightening ring and rotate it in the one direction or the other. Reliable clamping of the drill tool is assured by the locking mechanism during drilling under high load, especially during hammer drilling, even if strong vibrations act on the drill chuck. However, it should be noted that drill chucks are is increasingly also used for driving screws with battery-operated drills that are not connected to the line voltage. When driving screws the load on the drill chuck is distinctly reduced and the use of a locking mechanism is not obligatory. Since when chucking a tool, e.g. a screw bit, at first the jaws come to rest on the tool shaft and the locking mechanism is actuated with engagement of the locking member into the locking recess due to the increase of the resistance to rotation that then occurs, the locking member proceeds by degrees over the locking recesses until reaching the desired tightening force. This is associated with wear of the locking recesses as well as of the locking member that is unnecessary when using the drill chuck for driving screws.